Liquid fuel burners can be classified into two categories: atomizing burners and vaporizing burners. In an atomizing burner, combinations of high pressures and high velocity air are used to flow liquid fuel through an orifice and to break up the fuel into small droplets. The small droplets of fuel mix with air, vaporize and burn, usually more readily than larger droplets of fuel, due to surface-to-volume ratio effects. In a vaporizing burner, fuel is heated and vaporized without the aid of atomization. The vaporized fuel then mixes with air and burns. In some cases, electric heaters are used to help vaporize the fuel; in other cases, heat from the combustion process is sufficient to vaporize the fuel. Pre-heated air can also help vaporize fuel from a wick.
Gaseous fuel burners need not vaporize fuel since the fuel starts in the vapor phase. Many gaseous fuel burners pre-mix or partially pre-mix fuel and air prior to combustion. A flame can be stabilized using recirculation of hot exhaust products, or by the use of a bluff body, or by the use of a foam or a fibrous material to pre-heat the fuel-air mixture and then to stabilize the flame on the metal fiber or foam, or by the use of a swirling flow-field which can re-circulate exhaust products and stabilize the flame over large variations in supply velocity.